1. Field of the Invention
The present invention relates to a cryoablation catheter, and more particularly to a cryoablation catheter for creating long lesions.
2. Description of the Prior Art
Many medical procedures are performed using minimally invasive surgical techniques wherein one or more slender implements are inserted through one or more small incisions into a patient""s body. With respect to ablation, the surgical implement may include a rigid or flexible structure having an ablation device at or near its distal end that is placed adjacent to the tissue to be ablated. Radio frequency energy, microwave energy, laser energy, extreme heat, and extreme cold may be provided by the ablation device to destroy the tissue.
With respect to cardiac procedures, a cardiac arrhythmia may be treated through selective ablation of cardiac tissue to eliminate the source of the arrhythmia. A popular minimally invasive procedure, radio frequency (RF) catheter ablation, includes a preliminary step of conventional electrophysiology mapping followed by the creation of one or more ablated regions (lesions) in the cardiac tissue using RF energy. Multiple lesions are frequently required because the effectiveness of each of the lesion sites can not be predetermined with exactness due to limitations of conventional mapping. Often, five lesions, and sometimes as many as twenty lesions may be required before a successful result is attained. Usually only one of the lesions is actually effective.
Deficiencies of radio frequency ablation devices and techniques have been overcome by ice mapping prior to creating lesions, as taught by U.S. Pat. Nos. 5,423,807; 5,281,213 and 5,281,215. However, even though combined cryogenic mapping and ablation devices permit greater certainty and less tissue damage than RF devices and techniques, both the cryogenic and the RF devices are configured for spot or roughly circular tissue ablation.
Spot tissue ablation is acceptable for certain procedures. However, other procedures can be more therapeutically effective if multiple spot lesions are made along a predetermined line, or a single elongate or linear lesion is created in a single ablative step. Radio frequency ablation devices are known to be able to create linear lesions by dragging the ablation tip along a line while the ablation electrode is energized.
The present invention provides a cryogenic ablation system including a cryoablation catheter which is particularly well suited for creating elongated lesions.
In accordance with one aspect of the present invention, there is provided a cryoablation catheter which includes an outer tubular member capable of insertion into the vessels of the body, a sealing cap disposed at the distal end of the outer tubular member for forming a cooling chamber at the distal end of the catheter, and an inner tubular member which is slidably disposed within the outer tubular member. A fluid expansion nozzle is disposed on the distal end of the inner tubular member. The cryoablation catheter also includes a control means coupled to the proximal end of the inner tubular member for moving the inner tubular member longitudinally within the outer tubular member to thereby change the position of the fluid expansion nozzle within the cooling chamber. Preferably the fluid expansion nozzle takes the form of a Joule-Thompson nozzle. By moving the nozzle longitudinally within the cooling chamber it is possible to create a continuous long lesion along the entire length of the movement of the nozzle.
In accordance with another aspect of the present invention, the inner tubular member is disposed coaxially within the outer tubular member so as to define a passageway between the tubular members. A cylindrical support member is disposed between the inner tubular member and the outer tubular member and includes at least one aperture which extends through the support member to permit expanded fluid to return through the passageway to the proximal end of the catheter for removal from the system, or in a closed system for reprocessing for further use.
In accordance with still another aspect of the present invention, the control means takes the form of a control knob which is connected to the proximal end of the inner tubular member for controlling movement of the inner tubular member longitudinally within the outer tubular member to thereby change the position of the fluid expansion nozzle relative to the distal end of the cooling chamber.
These and other objects of the present invention will become more apparent when considered in view of the following description of a preferred embodiment of the present invention.